Platelet transfusion has become an integral part of the supportive care of cancer patients. Initially this was used in the treatment of patients with hematologic malignancies, but more recently, platelet transfusions have been widely used in the support cf patients with solid tumors treated with high dose chemotherapy, often accompanied by autologous marrow support. Improvements in blood component separation technology have made the use of platelet concentrates more readily available. Platelet concentrates are prepared by separating platelet rich plasma (PRP) from whole blood by gentle centrifugation followed by forceful centrifugation to compact platelets into a button which is resuspended in a small volume of plasma. Platelets are normally stored at 20.degree.-24.degree. C. (room temperature) for up to 5 days with continuous gentle agitation in gaspermeable plastic containers. (Snyder et al. Transfusion, 26:125-30, 1986)
Platelet concentrates are now a routine by-product of the collection of red blood cells and are prepared by either pooling 6 to 8 units per adult patient or by obtaining them through the process of plateletpheresis from an individual donor. However, with either method, platelets have a brief shelf-life and the "technique" of optimal platelet storage has not been resolved.
A great deal of meticulous work has evaluated and attempted to define the optimal conditions for storage of platelets. Factors which are important include temperature, pH of the plasma, which in turn depends upon the volume of the storage bag and gas exchange across the bag surface, mode of agitation, and the presence or absence of other cells in the storage product.
The difficulty of preserving platelets for future use without degrading their activity is well recognized in the art. The loss of activity is well documented in the literature e.g., Baythoon et al, J. Clin. Pathol., 35:870-874 (1982); Van Prooijen et al, Transfusion, 26:4 pp. 358-362; and Schiffer et al., Thrombos. Haemostas, 36:221-229 (1976).
During platelet preparation, platelets are activated and when stored for several days at room temperature they exhibit a variety of functional and morphological abnormalities including a poor response to aggregating agents and a lowering of the plasma pH. To maintain an acceptable pH during storage it is crucial that sufficient oxygen be able to enter the bag and that CO.sub.2 be able to diffuse out. A lack of oxygen entry into the storage container causes platelets to switch from aerobic to anaerobic metabolism with a resultant increase in the production of lactic acid which in turn is accompanied by an increase in pH. Agitation during storage is also considered necessary (Koerner K. Von Sang 44:37-41, 1983; Wallvil J. et al., Transfusion 30: 639-43, 1990) and although the mechanism behind the impairment of non agitated platelets is not understood, it has been suggested that gas exchange may be of major importance.
The prior art preservation techniques have included the preparation and use of frozen autologous platelets with and without dimethyl sulfoxide. Cryopreservation has not been generally accepted for storage with the exception of locations which stockpile matched donor platelets and autologous platelets for leukemia patients. The key issue affecting acceptance is the poor quality of the units after thawing.
The use of dimethyl sulfoxide has not been completely satisfactory because of irreversible changes in the platelets. Thrombos. Haemostas. (Stuttq.), 36 pp. 211-229 (1976).
Cryopreservation of platelets leads to severe reduction in the functional response of these cells. The nature of the defects underlying the deficient function of stored platelets is unclear. However, it is known that the platelets become activated during storage and it is believed that this activation induces the release of platelet ADP (adenosine diphosphate) which can cause irreversible or reversible changes in platelet membranes, thus, rendering them refractory to aggregating agents.
The applicant has discovered that if an adenosine-5'-triphosphatase and an adenosine-5'-diphosphatase is added to platelets prior to storage at room temperature with or without agitation or at cryotemperatures, the platelets have an improved response to ADP induced aggregation as compared to platelets which are stored without the additives. The invention provides for extended storage of platelets without substantial loss of activity which has been a characteristic of prior art preservation methods. The improved metabolic integrity as measured by plasma pH, pO.sub.2, pCO.sub.2 and hypotonic shock response (HRS) were maintained thoughout the storage period.
Accordingly it is a primary object of this invention to provide a method for the preservation of platelets at room temperature (20.degree. to 24.degree. C.) under standard agitation conditions as employed by blood banks or without agitiation under cryopreservation temperatures. (-70.degree. C. to -195.degree. C.)
It is also an object of this invention to provide a novel composition which has special utility in the preservation of platelets.
These and other objects of the invention will be apparent from the appended specification.